Telephone trunking system.



C. E. "STEPHENSON. TELEPHONE mums SYSTEM. APifLlCATlON FILED'FEB. 14, I912 1,172,402, 7 Patented Feb. 22,1916

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APPLICATION FILED FEB. 14, NHL

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TELEPHONE TRUNKING SYSTEM. APPLICATION FILED EEB.-14,'I9I2.

1 1 723:02. Patented Feb. 22, 1916.

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' In systems in which two-way "trunk lines UNITED sTATn:

CHARLES E. STEPHENSON, OF SIOUX CITY, IOWA, ASSIGNOR TO AUTOMATIC ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

'rntnrnonn TRUNKING sxs rnivr.

To all whom it may concern: I

Be it known that I, CHARLES E.- STEPHEN- soN, a citizen of the United States of are employed-that is, trunk lines over which a connection may be extended 1n either directionditficulty has been experienced in maintaining a properguarding potential upon the multiple terminals of said trunk at both ends thereof when said trunk is seized. Various systems .have been devised for accomplishing this result, but heretofore they have proved commercially unsatisfactory. l p One of the principal objects of my invention is the provision-o an nnproved system in which the selector bank contacts at each end of the trunk are provided .with guardmg potentials as soon as the trunk is seized at either end. I accomplish. this result without the employment of a third conductors of the trunk itselfductor in the trunk line, and supply the guarding potential for the opposite end of the trunk to that seized over one of the con- These and other objects of my invention will be more readily understood by reference to the accompanying drawings, in which Q Figures 1, 2 and 3 show a complete con-' nection between a'calling substation A and a called substation A in an automatic telephone system embodying the principles of my invention.

The automatic telephone system in connection with which I have chosen to illustrate myinvention is of the well-known tvpe of system embodying SUbSCIlbQI'S PIG- selector or line switches, selectors and con-'. nectors. The connection shown is extended from the substation A through its individual switch C at the central station to a first selector E, and through said selector E.

. Specification ofIetters Patent. t t b, 22;, 91 Application filed February s, 1912. Serial No. 677,532.

to'a repeater F in the same exchange, and thence over a trunk line comprising the conductors 2 and 3 tea second exchange. At the second'exchange the connection extends through a selector E and connector H to the, called substationA'. 'The trunk line, composed of the two conductors 2 and 3, which extends between the exchanges, is

a two-way trunk line'-that is, it may be used either for extending a connection from the exchange represented in Fig. 1 to the vice versa. At each exchange this trunk line is connected toa selector switch and a repeater, for example, the repeater F and the selector-E inFig. l,- and the repeater F and the selector E in Fig. 2. The subscribers individual or line-switch 0, its master switch D', the selector switches E, E, E and E and the connector H are of the well-known type of central office switching apparatus disclosed in. British exchange represented in Figs. 2 and 3,01

patent to W. James, No. 26,301 of 1906, and in the Westem-Electm'cirm of Chicago,

Illinois, ofJanuary 1T, '18 and 25, 1908. The construction of the selector and connector switches is also. disclosed in United States Letters Patent Nos. 815,321 and 815,176, respectively, granted March 13, 1906, to Keith, Erickson and Erickson. The selector E comprises the usual vertical and.

rotary line relays 21 and 22, the vertical magnet 90, rotary magnet 91,'releaserelay 25, release magnet 80, private magnet 92 and the side switch comprising the wipers 93, 94, 95 and 24. The selectors E and E are essentially the same as the selector E,

with the addition of one relay and twopairs of oif normal springs. (See the relay 53 and the springs 45 and 46 in the selector E theselector E The connector H comprises the usual vertical and rotary line reand the corresponding relay and springs in lays 63 and 64, vertical and rotary magnets 97 and 98, release magnet 75, private magnet 99, ringing relay 100 and side switch comprising the wipers 101, 102, 103 and 104. The selector E is similar to the selector E, with the addition of a bridge cut-oif relay 68. The selector E is individual to the line of the substation A, while the selector E is accessible in common to a plurality of substations through the medium of fair line 1 switches C.

The substations A and A' may be of any -through the medium. of an impulse wheel 6, the latter being in turn controlled by the calling subscriber through the medium of a dial (not shown) provided with finger holes. Such a substation is well known in the art, and it is not thought necessary to give a detailed description of the same herein. As is well known, when the calling device of a substation of this character is operated to call any digit, a preliminary ground. impulse is transmitted over the socalled rotary sideof the line from the substation to the central ofiice, then the vertical line isgrounded a number of times corresponding to the digit called, after which I contact in the banks of all the selectors the rotary line is grounded once more.

' The repeater F (Fig.1) is provided for the purpose of repeating impulses from the calling substation around the condensers 7 and 8 to the trunk conductors 2 and 3. The The relay 9 is adapted, when energized, to become locked in its operated position, from which it can be released by the energization of the magnet 10. The relay 11 is a slowacting relay.that is, a relay which is slow to deenergize after its energizing circuit has been broken. Therepeater F is in all respects the same as the repeater F.

In order to give a complete understanding of my invention, the complete operations by which the calling subscriber A obtains connection with the called subscriber A will now be explained. Since the operation of the switching apparatus disclosed herein is 1n general well known 1n the art, 1t is not thought necessary to describe ltS operatlon in detail, only sufiicient description. being his calling device for the first digit 2, the

preliminary impulse over the. rotary line conductor 12 passes through the springs of the cutoff relay 13 of the line switch C, and through the trip magnet14; to the battery lead 15, thence through battery B to ground G. leases the plunger of the line switch C, allowing it to enter its bank, whereby the line conductors 12 and 16 are extended through the line switch bank springs 17 and 18 and 19 and 20 to the selectorE. After the line switch C has operated, its master switch D operatesin a well-known manner to advance the plungers of the remaining line switches of the group to which. the switch C belongs to an idle trunk line. After the'connection The-magnet 14, upon. energizing, re

has thus been extended to the first selector E, two impulses are transmitted from. the substation A over the vertical line 16 and through the selector vertical line relay 21to the battery lead 15, followed by one impulse over the rotary line and' through the rotary line relay 22 of the selector. The selector E operates in response to these impulses transmitted through its verticaland rotary line relays to extend the line connection to an idle trunk line 23 leading to the distant exchange, which trunk line has associated with it in the exchange of the substation A the repeater F and selector E hen the connection is thus extended to this trunk line, the usual guarding ground is extendedto its selector private bank contacts fromground G in the selector E, through the side switch wiper 24, relay 25 and selector private wiper 2G to the bank contact 27 and the corresponding which have access to the same trunk line. From the selectorprivate bank contact 27 this ground potential also extends through -the relay springs 88 and 89 in the selector It will thus be seen that at the with the trunk line between exchanges, said trunk line is immediately protected from. being seized by any other selector switch, not only in the first exchange, but also in the second exchange as well.

W hen the calling device at the substation A is operated for the second digit 2, one im-- pulse is transmitted over the rotary line conductor 12, followed by two impulses over the vertical line 16 and. then by one more over the rotary line. The first impulse over the rotary line conductor 12 passes through the,line switch C and the first selector 'E, thence through the rotary line relay 38 of the repeater F and through the relay 39 to the battery lead 15. The relay 39 is energized by this impulse and operates to close the circuit of the relay 11, which operation is, however, without function at this time. The relay 38, upon energizing, completes a connection from. ground Gr through the springs 40 and 41 to the trunk conductor 3, which, however, is without effect, because the rotary line relay 4% of the selector E (Fig. 2) is disconnected from battery until after the switch shaft has been raised one or more steps from its vertical position. to

. through the permit the'springs and 46 to close their contacts. The two impulses for the second digit, which are transmitted over the vertical line conductor 16, pass through the switches G and E, thence through the repeater yertical line relay 47 and the relay 39 to the battery lead 15.- The relay 39, upon energizing, operates to close the circuit of the relay 11, which relay, upon energizing, disconnects the selector E from the trunk con-' ductors 2 and 3. The relay 11 being a slow acting relay does not have time to return to its normal position during the interval which elapses between the vertical impulses, and therefore maintains the selector E and the condensers 7 and 8 disconnected from the trunk during the entire time the impulses are being transmitted to the second exchange. The vertical relay 47, upon energizing, completes a circuitextending from ground Gr through the springs 40 and 48, thence over the trunk conductor 2 and springs 49 (Fig. 2), side switch wiper 50 and the selector vertical line relay 51 to the battery lead 52, thence through battery B to ground G. The relay 51, upon energizing, operates to close the circuit of the selector vertical magnet 82, which, upon energizing, operates to raise the switch shaft one step. Since the digit called is 2, the repeater vertical line relay 47' of the repeater F operates to transmit two impulses through the relay 51 of the selector E thereby causing the vertical magnet 82 to raisethe switch shaft two steps. Upon the first movement of the shaft of the selector E the springs 45 and 46 are permitted to close. Thesprings 45, upon closing, connect the rotary line relay 44 with the battery lead 52, while the springs 46, upon-closing, close thelcircuit of the relay 53. The relay 53, upon energizing, disconnects the selector private bank contact 34 of the trunk 23 from the trunk conductor 3 and supplies said contact with a new guarding ground which extends from ground G through the springs 54 and'33 to said contact. At the repeater F '(Fig. 1) the selector private bank contact 27 is disconnected from the trunk conductor 3.-by the first vertical impulse in the following manher: It will be seen that inthe repeater the relay 9 is normally connected with the vertical side of the line through its own springs Therefore, when the first impulse is transmitted to the repeater over the vertical side of the line, the relay 9 energizes and disconnects itself from the line, and its springs become locked in their operated positions by the engagement of the spring 29 with the catch 56. The separation of the springs 29 and 30 by the operation of the relay 9 disconnects the .private bank contacts from the rotary trunk conductor 3., When the final rotary impulse is transmitted over the rotary line 12, it energizes the repeater rotary pulse from ground G through the springs 40 and 41, trunk conductor 3, springs 57 (Fig. 2), side switch wiper 58, rotary line relay 44 of the selector E and springs 45 to the battery lead 52. The rotary line relay 44, upon energizing and deenergizing, transmits a single impulse through the private magnet 59, which latter operates in response thereto to cause the side switch to pass from first to second position, after which the rotary magnet 60 operates in a well-known manner'to rotate the wipers of the selector onto a trunk line leading to an idle connector H, after which the'side switch of the selector E passes to. third position in the usual manner;

The operation of the substation calling device for the last two digits of the called number causes the repeater F to operate in the same manner as just described to transmit the vertical and rotary impulses over the vertical and. rotary trunk conductors 2 and 3, respectively, and through the se lector E over the trunk conductors 61 and 62, thence through the connector vertical and rotary line relays'63 and ,64 to the battery lead 52. The connector H operates in response to these impulses in the usual and well-known manner to complete the connection with the called line. The entire talking circuit between the calling and the called substations is outlined by heavy conductors. lVhen thdconnection has been extended to the called line and the side switch of the connector passes to third-position, a guarding ground is extended to the connector private tion is released by the hanging up of the receiver at the calling substation. As the switch hook at the substation A descends, it momentarily presses together the springs 65, 66 and 67 thereby grounding both the vertical and rotary line conductors 12 and 16 simultaneously. This energizes both the line relays 47Jand 38 of the repeater F, which relays in turn operate to ground the trunk conductors 2 and 3 to energize the connector line relays 63 and 64. The relays 63 and 64, upon energizing, complete a circuit eX- tending from ground G at the selector E through the side switch wiper 69, relay 70, wiper 71, conductor 72, springs 73 and 74 and the connector release magnet 75; The magnet 75, upon energizing, immediately releases the connector H. .The relay 7 0, upon energizing, closes the circuit of the selector release magnet 85. At the repeater F the simultaneous nergization of the relays 47 and 38, besides grounding the trunk conductor 2, also completes a circuit extending from ground G at the selector E through the side switch wiper 2a, relay 25, wiper 26', contact 27, springs 78 and 79 and the relay 10 to the battery lead 15. The relay 10, upon energizing, operates to unlock the springs of the relay 9, while the relay'25 of the selector, upon energizing, closes the cir cuit of the selector release magnet 80. The magnet 80, upon energizing,cl0ses the circuit of the release magnet 81 of the line switch C. The release magnets 85, S0 and 81 of the switches. E and C, respectively, upon energizing, attract their armatures and hold them in readiness to release their respective switches when the switch hook at the substation descends far enough to permit the springs 65, 66 and 67 to separate, whereupon. the relaysdi'and 38 of the repeater and all relays and. magnets whose circuits were closed as a result of their energization become deenergized, and all switches employed in the connection are restored to nor mal position.

In the description of the operation of the two-way trunk line 23, it will be seen that the repeater F (Fig. 1) and the selector E (Fig. 2) were used, the selector. E? (Fig. 1; and the repeater F (Fig. :2) remaining moperative. Since both ends of the trunk line are exactlythe same, it will be evident that said trunk line could be used to extend a connection in the'opposite direction by being seized through the selector bank contacts 34, 35 and 3G in the second exchange.

The operation of the trunk line in this case 1. In a telephone system, a trunk line hay ing one or more line conductors extending from one end to the other of said trunk line,

automatic means for seizing one end of said trunk line, and a circuit including one of said line conductors for supplying a guarding potential to the opposite end of said trunk.

2. In a telephone system, a two-way trunk line having one or more line conductors extending from one end to the other of said trunk line, automatic means for seizing either end of said trunk line, and a circuit including one of said line conductors for supplying a guarding potential to the distant end or said trunk when either end of same is seized.

3. In a telephone system, a two-way trunk line, a plurality of multiple terminals for each end of said trunk line, automatic means for seizing either end of said trunk, and means for connecting aline conductor of said trunk with the multiple terminals at the distant ei d for placing a guarding p0- tential on the multiple terminals at the distant end thereof when either end of said trunk is seized. I v

at. In a telephone system, a two-way trunk line, an automatic selector switch at either end of said line for seizing the same, whereby connection can be extended over said trunk in either direction, and a guarding potential extending over a lineconductor of said trunk for preventing the selector at the distant end from seizing the same when one of said selectors has been operated to seize said trunk.

.In a telephone system, a two-way trunk having a plurality of multiple contacts at each end thereof, a plurality of automatic switches for seizing said trunk through said multiple contacts, and means for connecting one of the talking conductors of said trunk with the multiple terminals at the distant end for placlng .a guarding potential upon the multiple contacts at the distant end thereof when one of said switches operates to seize said trunk.

6. In a telephone system, a twoway trunk having multiple terminals at either end thereof. a selector for seizing one end of said. trunk through one of said multiple terminals, and a circuit including one of the talking conductors of said trunk for placing a guarding potential on the multiple terminals at the distant end thereof.

T. In a telephone system, a two-way trunk, means fOll seizing either end thereof, aselector and. a repeater at each end of said. trunk, means for operating said repeaters to transmit impulses over said'trunk tooperate the selector at the opposite end thereof, and

' a. circuit including one of the talking con-- ductors of said trunk for establishing a guarding potential when said trunk is seized to prevent the opposite end ofsaid trunk being seized.

8. In a telephone system, a two-way trunk having multiple terminals at each end thereof, means for seizing either end of a said trunk, a repeater and a selector for each end. of said trunk, means for operating said re-- peater torepeat impulses over said trunk having multiple terminals at eitherend thereof, means for seizing either end of said trunk, a selector associated with each end of said trunk for extending connection from said trunk, a circuit including a. line conductor of said trunk for'initially placing a guarding potential on the multiple contacts at the distant end of said trunk when one end of same is seized, and means for removing this guarding potential and placing a second guarding potential on said multiple terminalswhen the selector switch associated with the distant end of said trunk is operated.

10. In a telephone system, a two-way trunk having multiple terminals at either end thereof, means for seizing either. end of said trunk, an automatic switch associated with either end of said trunk for extending connection from said trunk, a circuit including one of the line conductors of said trunk 7 for establishing a guarding potential on the multiple terminals at the distant end thereof when said trunk is seized, and means for breaking this circuit and closing a second guarding potential circuit for said multiple terminals when the selector switchat the distant end of the trunk is moved from nor-, mal position.

.11. In a telephone system, a two-way trunk having multiple terminals at either end thereof, means for seizing either end of said trunk, a selector switch at each end of said trunk for, extending. connection there from, a pair of relays connected to opposite sides of said trunk line for controlling the operation of said selector switch, means for releasing said selector switch by simultaneously energizing said relays, a circuit including one side of said trunk line for establishing a guarding potential upon the multiple terminals at the opposite end thereof when one end of said .trunk line is seized, and an off normal switch for maintaining the circuit of the relay associated with the abovementioned side'of said trunk open when said selector switch is in normal position;

12. In a telephone system, a two-way trunk having multiple terminals at either end thereof, means for seizing either. end of said trunk, a selector switch for extending connection from either end of said trunk, a pair of relays connected to opposite sides of said trunk line for controlling the operation of said selector switch, means for] releasing said selector switch by simultaneously 'energizing'said relays, a circuit includin one side of said trunk line, for "establishing a guarding potential upon the multiple ter-' minals at the opposite end thereof when one end of said trunk line is seized, an off normal switch for maintaining the circuit of the relay associated with the above-mentioned side of said trunk whensaid switch is in normal position, and means for breaking said guarding potential circuit and establishing a second guarding potential circuit when said selector switch is moved from normal pos1-- tion.

13; In a telephone system, a two-way trunk having a plurality of multiple contacts at each end thereof, a plurality of automatic selecting switches for seizing said trunk, each of said switches having a bank of contacts including one of said multiple contacts, and means for connecting one of the talking conductors of said trunk with the multiple terminals at the distant end for placing a guarding potential upon the multiple contacts at the distant end thereof when one of said switches operates to seize.

said trunk, said selectors having one motion peater and asecond selector associated with each end of said trunk, means for operating one of said repeaters when the associated end of said trunk is seized to repeat 1m pulses over said'trunk to operate thesecond selector at the distant end thereof, and a circuit including a line conductor of said trunk for placing a guarding potential on the multiple terminals at the distant end thereof-to prevent the selecting switches at the distant end of said trunk from seizing the same, said selectors having one motion to select groups and a second motion to find a line in the selected group. v

15. In a telephone system, a two-way trunk having multiple terminals at either end thereof, a group of selecting switches at each end of said trunk for seizing the same, each'of said selectors having a bank of contacts including one of said multiple terminals, a second selector associated with each end of said trunk for extending a connection from said trunk, a circuit including a" line conductor of said trunk for initially placing a guarding potential on the multiple terminals at the distant. end thereof when one end of the same is seized, and

to find a line in the selected group.

16. In a telephone. system, a two-way trunk having multiple terminals at'either end thereof, a group of selectors at each end of said trunk for seizing the same, said selectors eachhaving a bank of contacts inmultiple terminals, a

cluding one of said at each end of said second selector switch trunk for extending connection therefrom, a pair ot relays connected to opposite sides of said trunk line for controlling the op tential upon the multiple terminals at the distant end thereof when one end of said trunk line is seized,-and an off normal switch for maintaining the circuit of the relay associated with the above-mentioned side ot'said trunk open when said second selector switch is in normal position, said selector switchesdiaving one motion to select groups and a secondmotion to find a line in a selected group.

17.111 a telephone system, a two-Way trunk having multiple terminals at either end thereof, a group of selectors at each endot' said trunk for seizing the same, said selectors 'each having a bank of -contacts including one ofsaid multiple terminals, a second selector switch ateach end of said trunk for extending connection therefrom, a pair of relays connected to opposite one side of said trunk linetor estabhshmg a guardlng posides or said trunk line for eontrollin g the operation ofsaid second SQ-lQPtOL switch, means for releasing said second selector switch by simultaneously energ :ing said relays, a circuit including one side (it said trunk line for establishing a guarding po-- tential upon the multiple terminals at the distant end thereof when one end of said trunk line is seized, an'otl normal switch for maintaining the circuit of the relay associated withthe above-mentioned side of said trunk .open when said second selector switch is in normal position.v and means for breaking said guarding potential circuit and establishing a second guarding potential 

